The lubrication of two-stroke cycle internal combustion engines is provided by an oil-fuel mixture. In this situation, the combustion characteristics of the oil which acts as a lubricant is as important as the lubricating characteristics of the oil in maintaining proper performance of the engine. While mineral lubricating oils provide a suitable source of the oil for use in such engines, these oils have a tendency to form combustion products which agglomerate to form deposits within the engine.
These deposits tend to cause excessive engine wear as well as spark plug fouling, ring sticking, and other difficulties.
Detergents are commonly added to lubricant compositions to prevent the deposition of solid materials on engine surfaces which come in contact with the lubricant composition. Lubricant compositions containing the ashless detergent prepared in accordance with the present invention are particularly satisfactory for use in a 2-stroke cycle gasoline engines. Such engines are becoming increasingly common and are found in chain saws, lawn mowers, outboard marine engines, and small cars or motor scooters.
It has been unexpectedly found that a detergent additive of improved characteristics useful in 2-stroke cycle engine lubricants can be prepared by reacting approximately 3 moles of isostearic acid with approximately 1 mole of tetraethylenepentamine. The imidazolines present in the products of this reaction are thereupon hydrolyzed with water to form amide reaction products. It has been found that the condensation reaction of isostearic acid with tetraethylenepentamine results in imidazolines. Unexpectedly, it has been found that when only amides are present in a detergent additive prepared in the procedure of the instant invention, the resulting detergent additive has improved detergent properties in an engine lubricant over detergent additives prepared in a conventional procedure.
It has long been known that lubricant detergent additives can be prepared by the reaction of a fatty acid with an amine. U.S. Pat. Nos. 3,110,673 and 3,169,980 teach the preparation of a lubricant composition from a mixed fatty acid and a polyamine. The fatty acid is a mixture of from 5 to about 30 mole percent of straight chain fatty acid and from about 70 to about 95 mole percent of branched chain fatty acid. The fatty acids contain from about 12 to about 30 carbon atoms. The polyamine is of the structure H.sub.2 N[R.sub.1 -N(R.sub.2)].sub.n R.sub.1 NH.sub.2 wherein R.sub.1 contains from 2 to 4 carbon atoms, R.sub.2 is hydrogen or an acyl group and n is an integer of from 1 to 5. The procedure of '673 teaches the reaction mix of the fatty acid mixture and polyamine are reacted according to known methods at conventional temperature for the usual period of time required to amidify the amino groups of the polyalkylene polyamine. Temperatures are in the range of from 250.degree. F. to 500.degree. F. Means of removing water of condensation is employed. U.S. Pat. No. 3,251,853 teaches an oil-soluble nitrogen-containing compound useful in lubricating oil compositions especially suitable for 2-stroke cycle engines. The nitrogen-containing compound is prepared by reacting at a temperature above 100.degree. C. a mixture comprising an amine selected from the group consisting of alkyl amines, aminoalkylamines and hydroxyalkyl amines with at least 0.5 equivalent of an acid producing compound of the structural formula RCOOH wherein R is a branched chain hydrocarbon radical having 14 to 20 saturated aliphatic carbon atoms in the principal chain and at least one lower acyclic pendant aliphatic group. The preferred relative proportions of the two reactants is one equivalent of the acid producing reactant to one to two equivalents of the amine. In some instances, as much as two equivalents of the acid producing reactant may be used for each equivalent of the amine. The unsaturated fatty acids from which the iso-aliphatic acids are obtained include oleic acid, lineoleic acid, linolenic acid or commercial fatty acid mixtures such as tall oil. The iso-aliphatic acid prepared from the above unsaturated acid is reacted with an amine, at a temperature preferably between 120.degree. C. and 250.degree. C. Water of reaction is removed. U.S. Pat. No. 3,405,064 teaches a lubricating oil composition containing a nitrogen-containing composition prepared by the method of U.S. Pat. No. 3,251,853.
Accordingly, in the prior art, there are teachings of the preparation of lubricant oil additives prepared from a reaction mixture of a fatty acid and an amine. However, there has been no recognition in the prior art that condensation of an isostearic acid with tetraethylene pentamine in a ratio of approximately 3 moles of acid to about 1 mole of amine, followed by hydrolysis of the resulting imidazoline groups to amides, resulted in an improved ashless detergent two-stroke cycle additive which maintains excellent engine cleanliness and has excellent low temperature stability.